Effects of invasive ants on the Japanese biota, and mechanisms underlying the expansion of their distribution

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The distribution of the Argentine ant, Linepithema humile, in Japan, and effect of the ant on the Japanese biota were investigated. Main results are as follow. 1.The distribution of the Argentine ant was investigated in 65 cities or towns along the Seto Inland Sea, western Japan. Our results include all available information of their distribution in Japan until 2005. Argentine ants have invaded Aichi Pref. (Tahara-shi), Hyogo Pref. (Kobe-shi), Hiroshima Pref. (Hiroshima-shi, Fuchu-cho, Hatsukaichi-shi, Ono-cho, Otake-shi), and Yamaguchi Pref. (Iwakuni-shi, Yanai-shi). The distribution range of Argentine ants in each area was limited to a few km except for the area in and around Hatsukaichi-shi. 2.The distribution of Argentine ants in urban parks around Hatsukaichi city was investigated from 2000 to 2005. The number of parks invaded by the ant increased from 27 to 41 during six years. 3.The Argentine ant invasion has remarkably reduced species richness of resident ants. Among 11 common epigeic species, nine species were vulnerable to Argentine ants, whereas Paratrechina sakurae and Camponotus vitiosus appeared less affected by this invasion. 4.Prey composition of the Japanese treefrog Hyla japonica was investigated in area invaded by Argentine ant Linepithema humile and area not invaded by the ant. In both area, ants were the most common taxa among prey animals in young treefrogs, constituting 82.4% of numeric proportion and 49.9% of volumetric proportion, and 42.8% of the numeric proportion and 25.7% of the volumetric proportion in invaded and uninvaded area, respectively. Among ants, the Argentine ant was most abundantin invaded area while Tetramorium tsushimae was the most common prey item in uninvaded area.